The present invention pertains generally to the field of semiconductors, and more particularly to a method of attaching electronic components to substrates.
In recent years, flip-chip and ball grid array techniques have increasingly been used to connect integrated circuit (IC) chips to interconnection substrates, such as printed circuit boards and to package substrates. In flip-chip bonding an IC chip component to a interconnection substrate or printed circuit board, a plurality (e.g., an array) of solder balls (also known as xe2x80x9csolder bumpsxe2x80x9d) are formed on a surface of a component, typically the IC chip component, and the bumped component is brought into a face-to-face relationship with the other component. The two components are then heated (such as in a furnace) to reflow (heat, then allow to cool) the solder bumps between the two components, thereby making electrical connections between respective terminals of the two components.
A need for ever finer pitch arrays of solder balls has accompanied an increase in the circuit density of IC chips and multi-chip modules. For example, an IC chip to be flip-chip connected to an interconnection substrate may require an array of 4 mil diameter solder balls disposed at an 8 mil pitch.
A xe2x80x9csolder ballxe2x80x9d refers to a substantially spherical or hemispherical mass or bump of solder (e.g., a lead-tin solder) resident on a substrate (e.g., electronic component), suitable for being re-flowed to join the electronic component to another electronic component. The term xe2x80x9cpitchxe2x80x9d refers to the distance between centers of adjacent solder balls on pads of a substrate. The following units and their equivalents are also used herein: 1 mil=0.001 inches; 1 micron=0.000001 meters; 25.4 microns=1 mil; 1 millimeter=0.001 meters.
As used herein, a xe2x80x9csubstratexe2x80x9d is an electronic component having a nominally flat surface upon which it is desirable to form solder balls to effect electrical connections to another electronic component. Ball grid array (BGA) substrates are substrates. As used herein, the terms xe2x80x9csubstrate bumpingxe2x80x9d and xe2x80x9cball bumpingxe2x80x9d refer to a process for forming solder balls on substrates.
The eutectic solder balls on heavy depopulated IC ball grid array packages tend to collapse excessively during reflow. This causes the balls to be short and wide, which can cause bridging problems and shorts.
Accordingly, there exists a need in the industry for a means to limit or control the collapse of eutectic solder balls during the reflow assembly process.
The apparatus comprise high melt balls on an electronic component surface to control the collapse of the eutectic solder balls on a BGA during the reflow process. The high melt balls also ensure coplanarity, consistent device standoff for rework, tighter pitch of solder balls and higher standoff for reliability.
A method for controlling the collapse of eutectic solder balls during the reflow manufacturing process by providing one or more high melt solder balls that limit the eutectic solder ball collapse and ensure coplanarity of the electronic component surface with the substrate surface.
An electronic assembly comprising an electronic component having a first surface attached to a first surface of a substrate, wherein the first surface of the electronic component is attached to the first surface of the substrate according to the following steps: forming an array of eutectic solder balls across the first surface of the electronic component; forming more than one high melt ball with a predetermined diameter on the first surface of the electronic component; bringing the eutectic solder balls into contact with the first surface of the substrate; and heating the eutectic solder balls without melting the high melt balls, such that the eutectic solder balls compress to the standoff of the diameter of the high melt balls.